Microelectromechanical systems (MEMS) include mechanical and electrical components having dimensions on the order of microns or smaller. MEMS structures are used in numerous applications including sensors and actuators.
The micromechanical component(s) in a sensor typically move in response to a condition (e.g., pressure, flow, acceleration and stress, amongst others). The sensor generates an electrical signal proportional to the movement which may be processed to provide a measurement of the condition. Actuators typically function by receiving an electric signal which generates an electrostatic force that can cause micromechanical components to move. Because the operation of a MEMS structure involves conducting electrical charge and the movement of small mechanical parts, it is desirable for MEMS components to be conductive and have sufficient mechanical integrity during use.
MEMS structures may be formed using microelectronic fabrication processes. In a typical process, deposition steps are used to deposit layers which are subsequently patterned using lithographic and etching steps to form the desired mechanical and electrical components. Other conventional processing steps, such as ion implantation, may also be employed if necessary.
Because microelectronic fabrication processes can be used to form MEMS structures, mechanical and electrical components of the structures are oftentimes formed of silicon. However, one disadvantage of silicon-based MEMS structures is the loss of performance under extreme conditions such as high temperatures, corrosive environments, or rapid vibrations. Under such conditions, the mechanical properties of silicon may be degraded so that the mechanical components cannot perform their desired function. Also, silicon becomes extrinsic at temperatures above 150° C. and, thus, loses its ability to function as a semiconductor material at such temperatures.